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Optical Coherence Tomography of the Anterior Segment in Eyes with Phakic Refractive Lenses
Optical Coherence Tomography of the Anterior Segment in Eyes with Phakic Refractive Lenses Annemari Koivula, MD, Maria Kugelberg, MD, PhD Purpose: To evaluate the dynamics of the phakic refractive lens (PRL) in myopic and hyperopic eyes in the nonaccommodated state and during subjective accommodation with Visante optical coherence tomography (OCT). Design: Cross-sectional study. Participants: Forty-one myopic eyes and 11 hyperopic eyes of 52 patients (mean age, 34 years; range, 24 – 49) were examined at least 1 year after PRL implantation using Visante OCT. Thirty-one myopic eyes had the PRL model 101 and 10 eyes had the smaller PRL model 100 implanted. The hyperopic model, PRL 200, is available in only one size. Methods: Noninvasive high-resolution anterior OCT was used to measure distance changes between the PRL and adjacent intraocular structures in the nonaccommodative state (baseline) and during accommodation. Main Outcome Measures: Mean distance changes from the anterior lens surface (ALS) to the PRL and from the corneal posterior surface to the ALS and the PRL, and changes in the pupil diameter. Results: At baseline, the mean distances between the PRL and crystalline lens were 0.38, 0.30, and 0.32 mm for the PRL 101, PRL 100, and PRL 200, respectively. The PRLs were significantly closer to the crystalline lens with increasing patient age. Three PRLs were in contact with the crystalline lens (6%), and there were lens opacities in 2 of these eyes. During accommodation, the ALS of all PRL models showed significant forward movement (P⬍0.05), whereas the distance between the PRL and crystalline lens decreased significantly with the PRL 101 and PRL 200 (P⬍0.05). The distance between the PRL 100 and crystalline lens remained unchanged during accommodation. Conclusion: The PRL moved forward during accommodation in all eyes, with the distance preserved between the PRL and the ALS with the PRL 100. The distance decreased with the other 2 models. In 85% of cases, there was no mechanical contact with the ALS during accommodation. Ophthalmology 2007;114: 2031–2037 © 2007 by the American Academy of Ophthalmology.
A primary concern with any type of posterior phakic intraocular lens (PIOL) is the risk of induced cataract.1–5 One of the primary risk factors for lens opacification seems to be direct mechanical contact with the lens, and therefore, the Originally received: January 4, 2007. Final revision: June 12, 2007. Accepted: June 12, 2007. Available online: August 31, 2007. Manuscript no. 2007-20. From the Anterior Segment Department, St. Erik’s Eye Hospital, and Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden. Presented at: XXIVth Congress of the European Society of Cataract and Refractive Surgeons, September 2006, London, United Kingdom, and American Society of Cataract and Refractive Surgery annual meeting, April 2007, San Diego, California. The authors have no proprietary or financial interest in any material, method, or product mentioned. Financial support was provided through the regional agreement on medical training and clinical research between Stockholm county council and the Karolinska Institute and St. Erik’s Ögonforskningsstiftelse. Correspondence and reprint requests to Annemari Koivula, MD, St. Erik’s Eye Hospital, S-11282 Stockholm, Sweden. E-mail: annemari.koivula@ sankterik.se. © 2007 by the American Academy of Ophthalmology Published by Elsevier Inc.
distance between the posterior PIOL and crystalline lens seems to be extremely important when evaluating different models of PIOLs.6 We previously evaluated the distance between the posterior surface of the phakic refractive lens (PS-PRL) and anterior lens surface (ALS) using the Scheimpflug technique and reported a significant decrease in this distance during the first year without changes during the second year.7 The disadvantage of the Scheimpflug method is the need for pupil dilation to obtain images of the entire surface of the crystalline lens and stimulation of the fellow eye to study accommodation of the eye under observation.8 Visante optical coherence tomography (OCT), a recently introduced device that allows noninvasive dynamic scanning and measurement of the anterior ocular segment,9 uses lowcoherence interferometry to provide in vivo cross-sectional images of tissue structures. The effect of accommodation can be studied easily by defocusing the target with negative lenses. In accommodation, the ALS moves forward and assumes a more rounded shape.10 With increasing age, the maximum possible change in lens movement declines.11 It can be assumed that in eyes with an implanted posterior PIOL, the PIOL comes closer to the crystalline lens during accommoISSN 0161-6420/07/$–see front matter doi:10.1016/j.ophtha.2007.06.020
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Ophthalmology Volume 114, Number 11, November 2007 Table 1. Summary of Patient Data Variable
PRL 101*
PRL 100*
PRL 200*
No. of eyes Mean age (yrs) (range) Mean PRL power (diopters) (range) Mean observation time (yrs) after implantation (range)
31 34 (24–49) ⫺6.3 (⫺3.5 to ⫺14.5) 2.6 (1.1–3.8)
10 34 (26–42) ⫺7.8 (⫺6.0 to ⫺10.0) 2.2 (1.0–3.4)
11 35 (30–45) ⫹6.3 (⫹3.5 to ⫹10.0) 2.6 (1.0–4.0)
*The phakic refractive lenses (PRLs) 101 and 100 are myopic PRL models, and PRL 200 is a hyperopic model.
dation, especially in nonpresbyopic eyes.6 However, the anterior chamber (AC) depth decreases throughout life approximately at the same rate as the lens axial thickness increases—that is, 13 m annually.11 The thickening of the lens could decrease the depth of the posterior chamber (PC), leaving less space for the PIOL in the PC. The current study was performed to investigate the movement of the PRL in relation to the behavior of the crystalline lens and pupil during accommodation. The correlation between age and PRL dynamics was investigated and the PRLs with lens contact were identified.
Patients and Methods Study Design
hyperopic PRL is manufactured in only one size and has an overall length of 10.6 mm.
Visante Optical Coherence Tomography Ophthalmic OCT was developed initially for retinal imaging, using a near-infrared 800-nm wavelength.12 For anterior segment imaging, a longer wavelength of 1300 nm allows greater penetration through highly scattering tissues, such as the limbus and sclera, and makes it possible to visualize angle structures.9 The technique works by splitting the light source into a reference and a measurement beam. The measurement beam from the ocular structures interacts with the reference light reflected from the reference mirror causing interference. The patient fixates on a target that is adjustable with positive or negative lenses, which are located within the OCT device, allowing compensation for the spherical ametropia. It is also possible to
The study population was comprised of 52 consecutive patients (52 eyes) with myopia and hyperopia, with the restriction for those who were unable to attend for personal reasons. The PRLs were implanted between April 2002 and May 2005 at the Department of Anterior Segment Surgery, St. Erik’s Eye Hospital, Stockholm, Sweden. Inclusion criteria included a minimum of 1 year after PRL surgery. Only one eye of each patient was enrolled in the study to avoid bias. An eye was excluded if any other refractive surgery was combined with PRL surgery. The study had a cross-sectional design in which all patients were scanned with Visante OCT only once without follow-up, and the association between the distance of the PRL from the ALS and lens opacification was investigated. The local ethics committee approved the study. All patients were provided with written and oral explanations of the study, and they all provided oral consent. Table 1 shows the different parameters of the study eyes.
Phakic Refractive Lens The PRL (Medennium Inc., Irvine, CA) is a thin silicone lens implanted in the PC to correct myopia or hyperopia. The lens floats and rotates in the PC without fixation in the sulcus. The haptics of the PRL rest on the zonules. The distance between the PRL and crystalline lens stabilized after the first year without changes during the second follow-up year (unpublished data). Therefore, a minimum of 1 year after PRL surgery was an inclusion criterion in the current study. The refractive range of the myopic implant is ⫺3.0 to ⫺20.0 diopters (D), and that of the hyperopic design is ⫹3.0 to ⫹15.0 D. Both are available in increments of 0.5 D. There are 2 sizes of myopic PRLs depending on the white-to-white diameter of the cornea: PRL 101, with a length of 11.3 mm for a white-to-white distance exceeding 11.3 mm, and PRL 100, with a length of 10.8 mm for a white-to-white distance between 10.5 and 11.3 mm. The
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Figure 1. Visante optical coherence tomography image of a hyperopic phakic refractive lens at baseline and during accommodation at ⫺3.0 and ⫺8.0 diopters (D).
Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs
Figure 2. After acquiring the scan, the measurement overlays are applied for analysis. Calibers are 2.38 mm for the vertical dimension between the anterior surface of the phakic refractive lens (PRL) and posterior corneal surface and 0.63 mm for between the posterior surface of the PRL and anterior lens surface. Software in Visante optical coherence tomography automatically finds the anterior and posterior corneal surfaces and highlights these surfaces with light blue lines. The central cornea thickness is 580 m. The horizontal dimension was placed behind the iris to indicate the length of the PRL 100 (10.8 mm).
defocus the target with negative lenses to induce physiologic accommodation in the examined eye. Once the eye is aligned, the anterior segment can be scanned several times at different degrees of accommodation, and the software restores the image to its actual dimensions, avoiding the errors induced by differences in ray transmission through the cornea (Fig 1). Measurements of the distance between 2 points, the curvature radius and the angles, are possible with the software.
Visante Optical Coherence Tomography as an Analytical Method To evaluate the precision of Visante OCT, a double-independent measurement study was conducted. Twenty-two eyes of 12 patients underwent scanning of the anterior segment of the eye; the scans were repeated after an interval of 5 minutes. The investigator evaluated the distances from the PS-PRL to the ALS and from the anterior surface of the PRL (AS-PRL) to the posterior corneal surface before the patient underwent a new scan (Fig 2). The second scan was analyzed later without knowledge of the results of the first scan. The results of the measurements are shown in Table 2, based on individual double-independent measurements. With Visante OCT, the variation of the single measurement between the PS-PRL and ALS was ⫾0.02 mm, with a random error of 5.0%; in the longer distance between the AS-PRL and the posterior corneal surface, it was ⫾0.03 mm, with a random error of 1.25%.
Main Outcome Measures Manifest refraction was tested before the OCT scans were performed to compensate for spherical ametropia during scanning. After scanning, the crystalline lens was examined after the pupils were dilated using tropicamide 0.5% to determine the presence of lens opacification. During all baseline examinations, the patients were asked to focus on a central target internal to the OCT device. Baseline measurements were performed in the nonaccommodated state at the horizontal meridian. All examinations were performed in a room with dim illumination. The eye was stimulated with negative lenses to achieve accommodation. The target was slowly defocused in ⫺0.25-D increTable 2. Double-Independent Data
Evaluated Distance PS-PRL to ALS AS-PRL to PCS
Mean Distance (mm)
Variation of a Single Measurement (mm)
Random Error (%)
10.42 2.72
⫾0.02 ⫾0.03
5.0 1.25
ALS ⫽ anterior lens surface; AS-PRL ⫽ anterior surface of the phakic refractive lens; PCS ⫽ posterior corneal surface; PS-PRL ⫽ posterior surface of the phakic refractive lens.
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Ophthalmology Volume 114, Number 11, November 2007 In hyperopic eyes implanted with the PRL 200, there was no contact with the crystalline lens at baseline. During accommodation, the PRL 200 was in contact in 3 cases (27%), and the distance decreased without contact in 6 cases (55%) and increased in 2 cases (18%). In myopic eyes, in the PRL 100 group one PRL (10%) touched the crystalline lens at baseline. The patient was a 42-year-old woman who had undergone surgery 3.4 years previously. The contact with the crystalline lens was found 1 day postoperatively without lens opacification. Follow-up with retroillumination photographs showed rotation of the PRL in the PC (Fig 4). Another PRL came in contact with the crystalline lens during accommodation (2 eyes [20%]), and the distance decreased without contact in 3 eyes (30%) and increased in 5 eyes (50%). In the myopic PRL 101 group, 2 PRLs (6%) had contact with the crystalline lens at baseline, and both eyes had anterior subcapsular opacification. These patients were the oldest in the study: a 48-year-old woman who had undergone PRL implantation 3 years previously and a 49-year-old man who had been implanted with the PRL 2 years previously. The woman developed unexpected hyperopia after the primary surgery. The PRL was exchanged with difficulty after 4 months, and anterior subcapsular opacification was observed 4 months after the second surgery without changes thereafter and without visual loss. In the man, lens opacification was detected at the time of OCT scanning (Fig 5). Six-month follow-up of this eye showed progressive opacification and loss of 1 line of best-corrected visual acuity. During accommodation, another PRL came in contact with the crystalline lens (for a total of 3 eyes [10%]). In 21 cases (68%), the distance decreased without contact; in 3 cases (10%), the distance increased; and in 4 eyes (13%), there was no change. The central thickness of the PRL did not change during accommodation in any eyes (Table 3) (P⬎0.05).
Correlation of the Distance between the Posterior Surface of the Phakic Refractive Lens and Anterior Lens Surface with Age
Figure 3. A myopic eye of a 33-year-old patient during accommodation. The target was slowly defocused with ⫺8.0 diopters (D) from the baseline (pushup method).
ments until it was subjectively blurred and could no longer be focused (pushup method) (Fig 3). The mean lens power added before blurred vision was achieved was ⫺4.6 D (range, ⫺1.25 to ⫺13.0).
Results
The mean patient ages and age ranges in the different groups are shown in Table 1. In Figure 6, the distance between the PS-PRL and ALS at baseline is plotted versus patient age. The initial distance was significantly lower in older eyes implanted with the PRL 101 (r ⫽ ⫺0.36; P⬍0.05). There was no significant trend in eyes implanted with the PRL 100 and 200 (rs ⫽ ⫺0.12 and 0.14, respectively; P⬎0.05).
Distances from the Posterior Corneal Surface to Anterior Lens Surface and Anterior Surface of the Phakic Refractive Lens The changes in the distances between the posterior corneal surface and ALS and the posterior corneal surface and AS-PRL were significant in all PRL models (Table 4) (P⬍0.05). The PRL 100 showed a larger change during accommodation than the other models, without significant differences among the groups.
Distance between the Posterior Surface of the Phakic Refractive Lens and Anterior Lens Surface
Change in Pupil Size during Accommodation
There was no significant difference in the initial distance between the different PRL types. During accommodation, with the PRL 200 and the PRL 101, there was a mean 84-m decrease in the distance between the PRL and crystalline lens. The distance between the PRL 100 and crystalline lens did not change during accommodation (Table 3). The differences were statistically significant when the confidence intervals (CIs) did not include zero.
The change in pupil diameter between baseline and accommodation was ⫺1.51⫾0.36 mm in the eyes with the PRL 101 (mean change ⫾ 95% CI), ⫺1.11⫾0.59 mm in eyes with the PRL 100, and ⫺1.59⫾0.60 mm in eyes with the PRL 200. The reduction was significant in all models (P⬍0.05). There was a correlation between the reduction in pupil diameter and reduction in the distance between the PS-PRL and ALS during accommodation in eyes with
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Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs
Figure 4. Retroillumination photographs of the phakic refractive lens model 100 show rotation of 52° between 1 week and 3 months postoperatively. The Scheimpflug images had revealed contact with the crystalline lens on the first postoperative day.
the PRL 200 (r ⫽ 0.67; P⬍0.05) but not in eyes with the PRL 101 and 100 (rs ⫽ 0.20 and ⫺0.41, respectively).
Discussion In the assessment of any new instrument, an estimate of the reproducibility is essential before further data analysis can be performed. The random error for the Scheimpflug method (with the EAS-1000 system [Nidek, Tokyo, Japan]) in the evaluation of the distance between the PRL and ALS was 10% (unpublished data). For Visante OCT, the same study design using double-independent measurements, repeated after an interval of 5 minutes, showed a random error of 5% in measurements between the PRL and crystalline lens and 1.25% in measurements between the PRL and posterior corneal surface. This result indicated that the Visante OCT is sufficiently accurate and reliable to allow an analysis of distances in the anterior segment and confirmed the results of a study with Visante OCT in measurements of the AC.13 Because the PRL does not change thickness during accommoda-
tion, the mean central thickness of the PRL in each group at baseline and during maximum accommodation served as an internal control. The results were comparable to the error analysis and confirmed the accuracy of the measurements. When investigating the movement of the PRL relative to adjacent intraocular structures in the current study, the main interest was the relation between the PRL and crystalline lens under different conditions, because the PRL has the potential to come into contact with the crystalline lens. Our previous PRL study showed a decrease of the initial distance between the PRL and crystalline lens over time, indicating a time-related interaction.7 This result was confirmed in a study with the Implantable Contact Lens (ICL; STAAR Surgical, Monrovia, CA).14 We found that the distance stabilized after 1 year, and this was an important inclusion criterion in the current study. During accommodation, significant forward movement of the ALS and PRL was observed in each group. Although the PRL moved anteriorly with accommodation with all 3 lens models, the space between the PRL and crystalline lens was preserved only with the PRL 100, and the space decreased with the other 2 models. The smaller size and weight of the PRL
Table 3. Mean Phakic Refractive Lens (PRL) Thickness and the Distance between the Posterior Surface of the Phakic Refractive Lens and the Anterior Lens Surface with 95% Confidence Interval at Baseline and during Accommodation Accommodation Baseline
PRL
n
Distance (mm)
PRL Thickness (mm)
PRL in Contact with the Lens
Cataract
Distance (mm)
Difference from Baseline (mm)
PRL Thickness (mm)
PRL in Contact with the Lens (Baseline ⫹ Accommodation)
101 100 200
31 10 11
0.38⫾0.07 0.30⫾0.14 0.32⫾0.09
0.105⫾0.030 0.090⫾0.019 0.343⫾0.071
2 1 0
2 0 0
0.29⫾0.09 0.31⫾0.19 0.23⫾0.14
⫺0.084⫾0.044* 0.002⫾0.100 ⫺0.083⫾0.074*
0.104⫾0.030 0.090⫾0.019 0.345⫾0.077
2⫹1 1⫹1 0⫹3
*P⬍0.05.
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Ophthalmology Volume 114, Number 11, November 2007
Figure 5. Progressive anterior subcapsular opacification in a myopic eye of a 49-year-old man.
100 may account for the difference in response to accommodation. Another force that pushes the posterior surface of the artificial lens toward the anterior surface of the crystalline lens is the pupil constriction resulting from light as reported by Petternel et al,15 who found a significantly reduced distance between the ICL and crystalline lens under photopic conditions, with pupil constriction. In the current study, there was significant pupil constriction during accommodation in all groups. In hyperopic eyes, the distance between the PRL and ALS decreased with pupil constriction, confirming the results from the ICL study, although the number of hyperopic cases was rather small. However,
pupil constriction in myopic eyes, as part of the accommodative process with lens changes, did not have the same effect as pupil constriction induced by light. Even if the pupil closed in front of the PRL, it did not push the myopic PRL backward to the crystalline lens. Lens thickening with age did not decrease the baseline distance between the PRL and crystalline lens in eyes with the PRL 100 and PRL 200. However, with the PRL 101 the initial gap decreased significantly with increasing age, indicating a smaller PC depth with aging of the lens. Two of the oldest PRL 101 cases in the study had central touch with the crystalline lens and developed lens opacification. These findings could confirm the results from ICL studies in which mechanical contact, presbyopic age, and intraoperative trauma are associated with an elevated incidence of crystalline lens opacification.2,3,16 In general, PRLs have been associated with a lower incidence of cataract than ICLs.7,17,18 To clarify the cause of secondary cataract after ICL implantation, Fujisawa et al studied aqueous circulation in the space between the ICL and crystalline lens in porcine eyes.19 When an ICL similar to the lens of the human eye was inserted into porcine eyes, anterior subcapsular opacities developed in all cases during the 3-month follow-up. No direct contact was observed between the ICL and crystalline lens at any time. The results suggest that the ICL altered the circulatory dynamics of the aqueous humor, probably because of poor circulation on the anterior surface of the crystalline lens, and resulted in cataract. There are structural and functional differences between human and porcine eyes, and results cannot be extrapolated directly to the human eye. However, the findings are interesting and could partly explain the difference in cataract incidence between ICL and PRL. In the current study, one myopic PRL 100 came in contact with the crystalline lens in the early postoperative period. The eye was followed with retroillumination photo-
Distance PRL-ALS in mm
0,9 0.9 0,8 0.8 0,7 0.7
PRL 101
0,6 0.6
PRL 100 PRL 200 r = -0.365 (PRL 101)
0,5 0.5 0,4 0.4
r = -0.116 (PRL 100) r = 0.139 (PRL 200)
0,3 0.3 0,2 0.2 0,1 0.1 0 20
30
40
50
Age Figure 6. There is a significant correlation between age and distance between the posterior surface of the phakic refractive lens (PRL) and anterior lens surface (ALS) at baseline in PRL 101 (P⬍0.05) but not in PRL 100 and 200.
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Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs Table 4. Mean Distance (Millimeters) from the Posterior Corneal Surface (PCS) to the Anterior Lens Surface (ALS) and the Anterior Surface of the Phakic Refractive Lens (AS-PRL) with 95% Confidence Interval at Baseline and during Accommodation Baseline PRL 101 100 200
n 31 10 11
PCS – ALS 3.31⫾0.10 2.97⫾0.16 2.98⫾0.15
Accommodation
PCS – AS-PRL 2.84⫾0.09 2.63⫾0.12 2.32⫾0.14
PCS – ALS 3.11⫾0.10 2.79⫾0.16 2.80⫾0.14
PCS – AS-PRL 2.72⫾0.11 2.40⫾0.23 2.22⫾0.18
Difference* PCS – ALS
PCS – AS-PRL
⫺0.194⫾0.046 ⫺0.174⫾0.0.06† ⫺0.176⫾0.074†
⫺0.121⫾0.062† ⫺0.228⫾0.143† ⫺0.102⫾0.074†
†
*Ninety-five percent confidence interval for the mean difference between baseline and accommodation. † P⬍0.05.
graphs that showed rotation of the PRL and indicated aqueous exchange behind the PRL. The floating design could be the characteristic of the PRL that protects against the development of lens opacities. The ICL is fixated in the ciliary sulcus and does not rotate.14 In conclusion, the PRL 100 preserved the distance to the ALS during accommodation, whereas it decreased in the 2 other models. However, in most cases there was no contact between the PRL and crystalline lens during accommodation. This finding combined with the floating design of the PRL could permit aqueous humor circulation to the anterior surface of the crystalline lens, resulting in less cataractogenesis than with the ICL. Contact with the crystalline lens and older age seemed to be risk factors for lens opacification.
References 1. Lackner B, Pieh S, Schmidinger G, et al. Outcome after treatment of ametropia with implantable contact lenses. Ophthalmology 2003;110:2153– 61. 2. Gonvers M, Bornet C, Othenin-Girard P. Implantable contact lens for moderate to high myopia: relationship of vaulting to cataract formation. J Cataract Refract Surg 2003;29:918 –24. 3. Lackner B, Pieh S, Schmidinger G, et al. Long-term results of implantation of phakic posterior chamber intraocular lenses. J Cataract Refract Surg 2004;30:2269 –76. 4. Fink AM, Gore C, Rosen E. Cataract development after implantation of the Staar Collamer posterior chamber phakic lens. J Cataract Refract Surg 1999;25:278 – 82. 5. Kohnen T. Cataract formation after implantation of myopic phakic posterior chamber IOLs. J Cataract Refract Surg 2004; 30:2245– 6. 6. Baikoff G, Lutun E, Wei J, Ferraz C. Contact between 3 phakic intraocular lens models and the crystalline lens: an anterior chamber optical coherence tomography study. J Cataract Refract Surg 2004;30:2007–12. 7. Koivula A, Petrelius A, Zetterstrom C. Clinical outcomes of phakic refractive lens in myopic and hyperopic eyes: 1-year results. J Cataract Refract Surg 2005;31:1145–52.
8. Koretz JF, Cook CA, Kaufman PL. Aging of the human lens: changes in lens shape upon accommodation and with accommodative loss. J Opt Soc Am A Opt Image Sci Vis 2002;19: 144 –51. 9. Radhakrishnan S, Rollins AM, Roth JE, et al. Real-time optical coherence tomography of the anterior segment at 1310 nm. Arch Ophthalmol 2001;119:1179 – 85. 10. Brown N. The change in shape and internal form of the lens of the eye on accommodation. Exp Eye Res 1973;15:441–59. 11. Koretz JF, Cook CA, Kaufman PL. Accommodation and presbyopia in the human eye: changes in the anterior segment and crystalline lens with focus. Invest Ophthalmol Vis Sci 1997;38:569 –78. 12. Hee MR, Puliafito CA, Duker JS, et al. Topography of diabetic macular edema with optical coherence tomography. Ophthalmology 1998;105:360 –70. 13. Kohnen T, Thomala MC, Cichocki M, Strenger A. Internal anterior chamber diameter using optical coherence tomography compared with white-to-white distances using automated measurements. J Cataract Refract Surg 2006;32:1809 –13. 14. Baumeister M, Buhren J, Kohnen T. Position of angle-supported, iris-fixated, and ciliary sulcus-implanted myopic phakic intraocular lenses evaluated by Scheimpflug photography. Am J Ophthalmol 2004;138:723–31. 15. Petternel V, Koppl CM, Dejaco-Ruhswurm I, et al. Effect of accommodation and pupil size on the movement of a posterior chamber lens in the phakic eye. Ophthalmology 2004;111: 325–31. 16. Sarikkola AU, Sen HN, Uusitalo RJ, Laatikainen L. Traumatic cataract and other adverse events with the implantable contact lens. J Cataract Refract Surg 2005;31:511–24. 17. Hoyos JE, Dementiev DD, Cigales M, et al. Phakic refractive lens experience in Spain. J Cataract Refract Surg 2002;28: 1939 – 46. 18. Pallikaris IG, Kalyvianaki MI, Kymionis GD, Panagopoulou SI. Phakic refractive lens implantation in high myopic patients: one-year results. J Cataract Refract Surg 2004;30: 1190 –7. 19. Fujisawa K, Shimizu K, Uga S, et al. Changes in the crystalline lens resulting from insertion of a phakic IOL (ICL) into the porcine eye. Graefes Arch Clin Exp Ophthalmol 2007;245:114 –22.
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A primary concern with any type of posterior phakic intraocular lens (PIOL) is the risk of induced cataract.1–5 One of the primary risk factors for lens opacification seems to be direct mechanical contact with the lens, and therefore, the Originally received: January 4, 2007. Final revision: June 12, 2007. Accepted: June 12, 2007. Available online: August 31, 2007. Manuscript no. 2007-20. From the Anterior Segment Department, St. Erik’s Eye Hospital, and Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden. Presented at: XXIVth Congress of the European Society of Cataract and Refractive Surgeons, September 2006, London, United Kingdom, and American Society of Cataract and Refractive Surgery annual meeting, April 2007, San Diego, California. The authors have no proprietary or financial interest in any material, method, or product mentioned. Financial support was provided through the regional agreement on medical training and clinical research between Stockholm county council and the Karolinska Institute and St. Erik’s Ögonforskningsstiftelse. Correspondence and reprint requests to Annemari Koivula, MD, St. Erik’s Eye Hospital, S-11282 Stockholm, Sweden. E-mail: annemari.koivula@ sankterik.se. © 2007 by the American Academy of Ophthalmology Published by Elsevier Inc.
distance between the posterior PIOL and crystalline lens seems to be extremely important when evaluating different models of PIOLs.6 We previously evaluated the distance between the posterior surface of the phakic refractive lens (PS-PRL) and anterior lens surface (ALS) using the Scheimpflug technique and reported a significant decrease in this distance during the first year without changes during the second year.7 The disadvantage of the Scheimpflug method is the need for pupil dilation to obtain images of the entire surface of the crystalline lens and stimulation of the fellow eye to study accommodation of the eye under observation.8 Visante optical coherence tomography (OCT), a recently introduced device that allows noninvasive dynamic scanning and measurement of the anterior ocular segment,9 uses lowcoherence interferometry to provide in vivo cross-sectional images of tissue structures. The effect of accommodation can be studied easily by defocusing the target with negative lenses. In accommodation, the ALS moves forward and assumes a more rounded shape.10 With increasing age, the maximum possible change in lens movement declines.11 It can be assumed that in eyes with an implanted posterior PIOL, the PIOL comes closer to the crystalline lens during accommoISSN 0161-6420/07/$–see front matter doi:10.1016/j.ophtha.2007.06.020
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Ophthalmology Volume 114, Number 11, November 2007 Table 1. Summary of Patient Data Variable
PRL 101*
PRL 100*
PRL 200*
No. of eyes Mean age (yrs) (range) Mean PRL power (diopters) (range) Mean observation time (yrs) after implantation (range)
31 34 (24–49) ⫺6.3 (⫺3.5 to ⫺14.5) 2.6 (1.1–3.8)
10 34 (26–42) ⫺7.8 (⫺6.0 to ⫺10.0) 2.2 (1.0–3.4)
11 35 (30–45) ⫹6.3 (⫹3.5 to ⫹10.0) 2.6 (1.0–4.0)
*The phakic refractive lenses (PRLs) 101 and 100 are myopic PRL models, and PRL 200 is a hyperopic model.
dation, especially in nonpresbyopic eyes.6 However, the anterior chamber (AC) depth decreases throughout life approximately at the same rate as the lens axial thickness increases—that is, 13 m annually.11 The thickening of the lens could decrease the depth of the posterior chamber (PC), leaving less space for the PIOL in the PC. The current study was performed to investigate the movement of the PRL in relation to the behavior of the crystalline lens and pupil during accommodation. The correlation between age and PRL dynamics was investigated and the PRLs with lens contact were identified.
Patients and Methods Study Design
hyperopic PRL is manufactured in only one size and has an overall length of 10.6 mm.
Visante Optical Coherence Tomography Ophthalmic OCT was developed initially for retinal imaging, using a near-infrared 800-nm wavelength.12 For anterior segment imaging, a longer wavelength of 1300 nm allows greater penetration through highly scattering tissues, such as the limbus and sclera, and makes it possible to visualize angle structures.9 The technique works by splitting the light source into a reference and a measurement beam. The measurement beam from the ocular structures interacts with the reference light reflected from the reference mirror causing interference. The patient fixates on a target that is adjustable with positive or negative lenses, which are located within the OCT device, allowing compensation for the spherical ametropia. It is also possible to
The study population was comprised of 52 consecutive patients (52 eyes) with myopia and hyperopia, with the restriction for those who were unable to attend for personal reasons. The PRLs were implanted between April 2002 and May 2005 at the Department of Anterior Segment Surgery, St. Erik’s Eye Hospital, Stockholm, Sweden. Inclusion criteria included a minimum of 1 year after PRL surgery. Only one eye of each patient was enrolled in the study to avoid bias. An eye was excluded if any other refractive surgery was combined with PRL surgery. The study had a cross-sectional design in which all patients were scanned with Visante OCT only once without follow-up, and the association between the distance of the PRL from the ALS and lens opacification was investigated. The local ethics committee approved the study. All patients were provided with written and oral explanations of the study, and they all provided oral consent. Table 1 shows the different parameters of the study eyes.
Phakic Refractive Lens The PRL (Medennium Inc., Irvine, CA) is a thin silicone lens implanted in the PC to correct myopia or hyperopia. The lens floats and rotates in the PC without fixation in the sulcus. The haptics of the PRL rest on the zonules. The distance between the PRL and crystalline lens stabilized after the first year without changes during the second follow-up year (unpublished data). Therefore, a minimum of 1 year after PRL surgery was an inclusion criterion in the current study. The refractive range of the myopic implant is ⫺3.0 to ⫺20.0 diopters (D), and that of the hyperopic design is ⫹3.0 to ⫹15.0 D. Both are available in increments of 0.5 D. There are 2 sizes of myopic PRLs depending on the white-to-white diameter of the cornea: PRL 101, with a length of 11.3 mm for a white-to-white distance exceeding 11.3 mm, and PRL 100, with a length of 10.8 mm for a white-to-white distance between 10.5 and 11.3 mm. The
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Figure 1. Visante optical coherence tomography image of a hyperopic phakic refractive lens at baseline and during accommodation at ⫺3.0 and ⫺8.0 diopters (D).
Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs
Figure 2. After acquiring the scan, the measurement overlays are applied for analysis. Calibers are 2.38 mm for the vertical dimension between the anterior surface of the phakic refractive lens (PRL) and posterior corneal surface and 0.63 mm for between the posterior surface of the PRL and anterior lens surface. Software in Visante optical coherence tomography automatically finds the anterior and posterior corneal surfaces and highlights these surfaces with light blue lines. The central cornea thickness is 580 m. The horizontal dimension was placed behind the iris to indicate the length of the PRL 100 (10.8 mm).
defocus the target with negative lenses to induce physiologic accommodation in the examined eye. Once the eye is aligned, the anterior segment can be scanned several times at different degrees of accommodation, and the software restores the image to its actual dimensions, avoiding the errors induced by differences in ray transmission through the cornea (Fig 1). Measurements of the distance between 2 points, the curvature radius and the angles, are possible with the software.
Visante Optical Coherence Tomography as an Analytical Method To evaluate the precision of Visante OCT, a double-independent measurement study was conducted. Twenty-two eyes of 12 patients underwent scanning of the anterior segment of the eye; the scans were repeated after an interval of 5 minutes. The investigator evaluated the distances from the PS-PRL to the ALS and from the anterior surface of the PRL (AS-PRL) to the posterior corneal surface before the patient underwent a new scan (Fig 2). The second scan was analyzed later without knowledge of the results of the first scan. The results of the measurements are shown in Table 2, based on individual double-independent measurements. With Visante OCT, the variation of the single measurement between the PS-PRL and ALS was ⫾0.02 mm, with a random error of 5.0%; in the longer distance between the AS-PRL and the posterior corneal surface, it was ⫾0.03 mm, with a random error of 1.25%.
Main Outcome Measures Manifest refraction was tested before the OCT scans were performed to compensate for spherical ametropia during scanning. After scanning, the crystalline lens was examined after the pupils were dilated using tropicamide 0.5% to determine the presence of lens opacification. During all baseline examinations, the patients were asked to focus on a central target internal to the OCT device. Baseline measurements were performed in the nonaccommodated state at the horizontal meridian. All examinations were performed in a room with dim illumination. The eye was stimulated with negative lenses to achieve accommodation. The target was slowly defocused in ⫺0.25-D increTable 2. Double-Independent Data
Evaluated Distance PS-PRL to ALS AS-PRL to PCS
Mean Distance (mm)
Variation of a Single Measurement (mm)
Random Error (%)
10.42 2.72
⫾0.02 ⫾0.03
5.0 1.25
ALS ⫽ anterior lens surface; AS-PRL ⫽ anterior surface of the phakic refractive lens; PCS ⫽ posterior corneal surface; PS-PRL ⫽ posterior surface of the phakic refractive lens.
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Ophthalmology Volume 114, Number 11, November 2007 In hyperopic eyes implanted with the PRL 200, there was no contact with the crystalline lens at baseline. During accommodation, the PRL 200 was in contact in 3 cases (27%), and the distance decreased without contact in 6 cases (55%) and increased in 2 cases (18%). In myopic eyes, in the PRL 100 group one PRL (10%) touched the crystalline lens at baseline. The patient was a 42-year-old woman who had undergone surgery 3.4 years previously. The contact with the crystalline lens was found 1 day postoperatively without lens opacification. Follow-up with retroillumination photographs showed rotation of the PRL in the PC (Fig 4). Another PRL came in contact with the crystalline lens during accommodation (2 eyes [20%]), and the distance decreased without contact in 3 eyes (30%) and increased in 5 eyes (50%). In the myopic PRL 101 group, 2 PRLs (6%) had contact with the crystalline lens at baseline, and both eyes had anterior subcapsular opacification. These patients were the oldest in the study: a 48-year-old woman who had undergone PRL implantation 3 years previously and a 49-year-old man who had been implanted with the PRL 2 years previously. The woman developed unexpected hyperopia after the primary surgery. The PRL was exchanged with difficulty after 4 months, and anterior subcapsular opacification was observed 4 months after the second surgery without changes thereafter and without visual loss. In the man, lens opacification was detected at the time of OCT scanning (Fig 5). Six-month follow-up of this eye showed progressive opacification and loss of 1 line of best-corrected visual acuity. During accommodation, another PRL came in contact with the crystalline lens (for a total of 3 eyes [10%]). In 21 cases (68%), the distance decreased without contact; in 3 cases (10%), the distance increased; and in 4 eyes (13%), there was no change. The central thickness of the PRL did not change during accommodation in any eyes (Table 3) (P⬎0.05).
Correlation of the Distance between the Posterior Surface of the Phakic Refractive Lens and Anterior Lens Surface with Age
Figure 3. A myopic eye of a 33-year-old patient during accommodation. The target was slowly defocused with ⫺8.0 diopters (D) from the baseline (pushup method).
ments until it was subjectively blurred and could no longer be focused (pushup method) (Fig 3). The mean lens power added before blurred vision was achieved was ⫺4.6 D (range, ⫺1.25 to ⫺13.0).
Results
The mean patient ages and age ranges in the different groups are shown in Table 1. In Figure 6, the distance between the PS-PRL and ALS at baseline is plotted versus patient age. The initial distance was significantly lower in older eyes implanted with the PRL 101 (r ⫽ ⫺0.36; P⬍0.05). There was no significant trend in eyes implanted with the PRL 100 and 200 (rs ⫽ ⫺0.12 and 0.14, respectively; P⬎0.05).
Distances from the Posterior Corneal Surface to Anterior Lens Surface and Anterior Surface of the Phakic Refractive Lens The changes in the distances between the posterior corneal surface and ALS and the posterior corneal surface and AS-PRL were significant in all PRL models (Table 4) (P⬍0.05). The PRL 100 showed a larger change during accommodation than the other models, without significant differences among the groups.
Distance between the Posterior Surface of the Phakic Refractive Lens and Anterior Lens Surface
Change in Pupil Size during Accommodation
There was no significant difference in the initial distance between the different PRL types. During accommodation, with the PRL 200 and the PRL 101, there was a mean 84-m decrease in the distance between the PRL and crystalline lens. The distance between the PRL 100 and crystalline lens did not change during accommodation (Table 3). The differences were statistically significant when the confidence intervals (CIs) did not include zero.
The change in pupil diameter between baseline and accommodation was ⫺1.51⫾0.36 mm in the eyes with the PRL 101 (mean change ⫾ 95% CI), ⫺1.11⫾0.59 mm in eyes with the PRL 100, and ⫺1.59⫾0.60 mm in eyes with the PRL 200. The reduction was significant in all models (P⬍0.05). There was a correlation between the reduction in pupil diameter and reduction in the distance between the PS-PRL and ALS during accommodation in eyes with
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Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs
Figure 4. Retroillumination photographs of the phakic refractive lens model 100 show rotation of 52° between 1 week and 3 months postoperatively. The Scheimpflug images had revealed contact with the crystalline lens on the first postoperative day.
the PRL 200 (r ⫽ 0.67; P⬍0.05) but not in eyes with the PRL 101 and 100 (rs ⫽ 0.20 and ⫺0.41, respectively).
Discussion In the assessment of any new instrument, an estimate of the reproducibility is essential before further data analysis can be performed. The random error for the Scheimpflug method (with the EAS-1000 system [Nidek, Tokyo, Japan]) in the evaluation of the distance between the PRL and ALS was 10% (unpublished data). For Visante OCT, the same study design using double-independent measurements, repeated after an interval of 5 minutes, showed a random error of 5% in measurements between the PRL and crystalline lens and 1.25% in measurements between the PRL and posterior corneal surface. This result indicated that the Visante OCT is sufficiently accurate and reliable to allow an analysis of distances in the anterior segment and confirmed the results of a study with Visante OCT in measurements of the AC.13 Because the PRL does not change thickness during accommoda-
tion, the mean central thickness of the PRL in each group at baseline and during maximum accommodation served as an internal control. The results were comparable to the error analysis and confirmed the accuracy of the measurements. When investigating the movement of the PRL relative to adjacent intraocular structures in the current study, the main interest was the relation between the PRL and crystalline lens under different conditions, because the PRL has the potential to come into contact with the crystalline lens. Our previous PRL study showed a decrease of the initial distance between the PRL and crystalline lens over time, indicating a time-related interaction.7 This result was confirmed in a study with the Implantable Contact Lens (ICL; STAAR Surgical, Monrovia, CA).14 We found that the distance stabilized after 1 year, and this was an important inclusion criterion in the current study. During accommodation, significant forward movement of the ALS and PRL was observed in each group. Although the PRL moved anteriorly with accommodation with all 3 lens models, the space between the PRL and crystalline lens was preserved only with the PRL 100, and the space decreased with the other 2 models. The smaller size and weight of the PRL
Table 3. Mean Phakic Refractive Lens (PRL) Thickness and the Distance between the Posterior Surface of the Phakic Refractive Lens and the Anterior Lens Surface with 95% Confidence Interval at Baseline and during Accommodation Accommodation Baseline
PRL
n
Distance (mm)
PRL Thickness (mm)
PRL in Contact with the Lens
Cataract
Distance (mm)
Difference from Baseline (mm)
PRL Thickness (mm)
PRL in Contact with the Lens (Baseline ⫹ Accommodation)
101 100 200
31 10 11
0.38⫾0.07 0.30⫾0.14 0.32⫾0.09
0.105⫾0.030 0.090⫾0.019 0.343⫾0.071
2 1 0
2 0 0
0.29⫾0.09 0.31⫾0.19 0.23⫾0.14
⫺0.084⫾0.044* 0.002⫾0.100 ⫺0.083⫾0.074*
0.104⫾0.030 0.090⫾0.019 0.345⫾0.077
2⫹1 1⫹1 0⫹3
*P⬍0.05.
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Ophthalmology Volume 114, Number 11, November 2007
Figure 5. Progressive anterior subcapsular opacification in a myopic eye of a 49-year-old man.
100 may account for the difference in response to accommodation. Another force that pushes the posterior surface of the artificial lens toward the anterior surface of the crystalline lens is the pupil constriction resulting from light as reported by Petternel et al,15 who found a significantly reduced distance between the ICL and crystalline lens under photopic conditions, with pupil constriction. In the current study, there was significant pupil constriction during accommodation in all groups. In hyperopic eyes, the distance between the PRL and ALS decreased with pupil constriction, confirming the results from the ICL study, although the number of hyperopic cases was rather small. However,
pupil constriction in myopic eyes, as part of the accommodative process with lens changes, did not have the same effect as pupil constriction induced by light. Even if the pupil closed in front of the PRL, it did not push the myopic PRL backward to the crystalline lens. Lens thickening with age did not decrease the baseline distance between the PRL and crystalline lens in eyes with the PRL 100 and PRL 200. However, with the PRL 101 the initial gap decreased significantly with increasing age, indicating a smaller PC depth with aging of the lens. Two of the oldest PRL 101 cases in the study had central touch with the crystalline lens and developed lens opacification. These findings could confirm the results from ICL studies in which mechanical contact, presbyopic age, and intraoperative trauma are associated with an elevated incidence of crystalline lens opacification.2,3,16 In general, PRLs have been associated with a lower incidence of cataract than ICLs.7,17,18 To clarify the cause of secondary cataract after ICL implantation, Fujisawa et al studied aqueous circulation in the space between the ICL and crystalline lens in porcine eyes.19 When an ICL similar to the lens of the human eye was inserted into porcine eyes, anterior subcapsular opacities developed in all cases during the 3-month follow-up. No direct contact was observed between the ICL and crystalline lens at any time. The results suggest that the ICL altered the circulatory dynamics of the aqueous humor, probably because of poor circulation on the anterior surface of the crystalline lens, and resulted in cataract. There are structural and functional differences between human and porcine eyes, and results cannot be extrapolated directly to the human eye. However, the findings are interesting and could partly explain the difference in cataract incidence between ICL and PRL. In the current study, one myopic PRL 100 came in contact with the crystalline lens in the early postoperative period. The eye was followed with retroillumination photo-
Distance PRL-ALS in mm
0,9 0.9 0,8 0.8 0,7 0.7
PRL 101
0,6 0.6
PRL 100 PRL 200 r = -0.365 (PRL 101)
0,5 0.5 0,4 0.4
r = -0.116 (PRL 100) r = 0.139 (PRL 200)
0,3 0.3 0,2 0.2 0,1 0.1 0 20
30
40
50
Age Figure 6. There is a significant correlation between age and distance between the posterior surface of the phakic refractive lens (PRL) and anterior lens surface (ALS) at baseline in PRL 101 (P⬍0.05) but not in PRL 100 and 200.
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Koivula and Kugelberg 䡠 OCT of the Anterior Segment in Eyes with PRLs Table 4. Mean Distance (Millimeters) from the Posterior Corneal Surface (PCS) to the Anterior Lens Surface (ALS) and the Anterior Surface of the Phakic Refractive Lens (AS-PRL) with 95% Confidence Interval at Baseline and during Accommodation Baseline PRL 101 100 200
n 31 10 11
PCS – ALS 3.31⫾0.10 2.97⫾0.16 2.98⫾0.15
Accommodation
PCS – AS-PRL 2.84⫾0.09 2.63⫾0.12 2.32⫾0.14
PCS – ALS 3.11⫾0.10 2.79⫾0.16 2.80⫾0.14
PCS – AS-PRL 2.72⫾0.11 2.40⫾0.23 2.22⫾0.18
Difference* PCS – ALS
PCS – AS-PRL
⫺0.194⫾0.046 ⫺0.174⫾0.0.06† ⫺0.176⫾0.074†
⫺0.121⫾0.062† ⫺0.228⫾0.143† ⫺0.102⫾0.074†
†
*Ninety-five percent confidence interval for the mean difference between baseline and accommodation. † P⬍0.05.
graphs that showed rotation of the PRL and indicated aqueous exchange behind the PRL. The floating design could be the characteristic of the PRL that protects against the development of lens opacities. The ICL is fixated in the ciliary sulcus and does not rotate.14 In conclusion, the PRL 100 preserved the distance to the ALS during accommodation, whereas it decreased in the 2 other models. However, in most cases there was no contact between the PRL and crystalline lens during accommodation. This finding combined with the floating design of the PRL could permit aqueous humor circulation to the anterior surface of the crystalline lens, resulting in less cataractogenesis than with the ICL. Contact with the crystalline lens and older age seemed to be risk factors for lens opacification.
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8. Koretz JF, Cook CA, Kaufman PL. Aging of the human lens: changes in lens shape upon accommodation and with accommodative loss. J Opt Soc Am A Opt Image Sci Vis 2002;19: 144 –51. 9. Radhakrishnan S, Rollins AM, Roth JE, et al. Real-time optical coherence tomography of the anterior segment at 1310 nm. Arch Ophthalmol 2001;119:1179 – 85. 10. Brown N. The change in shape and internal form of the lens of the eye on accommodation. Exp Eye Res 1973;15:441–59. 11. Koretz JF, Cook CA, Kaufman PL. Accommodation and presbyopia in the human eye: changes in the anterior segment and crystalline lens with focus. Invest Ophthalmol Vis Sci 1997;38:569 –78. 12. Hee MR, Puliafito CA, Duker JS, et al. Topography of diabetic macular edema with optical coherence tomography. Ophthalmology 1998;105:360 –70. 13. Kohnen T, Thomala MC, Cichocki M, Strenger A. Internal anterior chamber diameter using optical coherence tomography compared with white-to-white distances using automated measurements. J Cataract Refract Surg 2006;32:1809 –13. 14. Baumeister M, Buhren J, Kohnen T. Position of angle-supported, iris-fixated, and ciliary sulcus-implanted myopic phakic intraocular lenses evaluated by Scheimpflug photography. Am J Ophthalmol 2004;138:723–31. 15. Petternel V, Koppl CM, Dejaco-Ruhswurm I, et al. Effect of accommodation and pupil size on the movement of a posterior chamber lens in the phakic eye. Ophthalmology 2004;111: 325–31. 16. Sarikkola AU, Sen HN, Uusitalo RJ, Laatikainen L. Traumatic cataract and other adverse events with the implantable contact lens. J Cataract Refract Surg 2005;31:511–24. 17. Hoyos JE, Dementiev DD, Cigales M, et al. Phakic refractive lens experience in Spain. J Cataract Refract Surg 2002;28: 1939 – 46. 18. Pallikaris IG, Kalyvianaki MI, Kymionis GD, Panagopoulou SI. Phakic refractive lens implantation in high myopic patients: one-year results. J Cataract Refract Surg 2004;30: 1190 –7. 19. Fujisawa K, Shimizu K, Uga S, et al. Changes in the crystalline lens resulting from insertion of a phakic IOL (ICL) into the porcine eye. Graefes Arch Clin Exp Ophthalmol 2007;245:114 –22.
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